Tires are designed to handle a wide range of driving conditions. Engineers create designs for off road, high performance, heavy load carrying and all-season driving conditions, to name a few. As a result of the variety of tire types, the manufacturing process must be able to produce a wide variety of rubber compounds and components that when combined into a tire will perform to help meet the customer’s requirements. The manufacturing process consists of the following primary steps:
- Mixing. Natural and synthetic rubbers are mixed with many other chemicals to create a compound that serves a particular purpose within the tire. There are many versions of rubber compounds based on location in the tire and the tire performance desired. All the ingredients are mixed in specific amounts per a specification for use it the next steps.
- Extrusion. Some of the rubber that leaves mixing goes to the extruders. Here rubber is pushed through a die to create shapes made of one or more different compounds in different locations to be used in the tire. Examples would be the tread and sidewall extrusions.
- Calendering. In this process rubber is either calendered, or pressed, into a rubber sheet or impregnated into fabric or steel to create a rubber coated reinforced sheet to be cut into components for the tire. Examples of these components include the inner liner, body plies, and belts. There are many versions of fabric and steel as well as compounds used based on the type and service of the tire.
- Tire Building. The tire itself is a very complex composite of materials. Tire building takes all the components listed on the specification which were produced in the previous steps and puts them together to create the uncured (green) tire. The tire is assembled from the inside out by wrapping the components around a drum and forcing them together using internal air pressure and rollers pressing from the outside to consolidate the components together.
- Curing. The curing process is where the tire becomes the tire as consumers know it. Here the uncured or green tire is placed into a mold which is mounted into a press. Once the tire is loaded into the press a bladder inflates into the tire at low pressure to hold the tire in place as the mold closes around the tire. Once closed, high pressure steam or gas fills the bladder forcing the tire into the mold to take the final shape of the tire. The proper time, temperature and pressures are listed on the specification for curing the tire and are determined by running thermocouple tests to set the optimal cure setup.
- Measuring and Testing. Once the tire is cured it is not quite ready to send to a waiting customer. First it goes to a machine where it is inflated and ran against a wheel at a certain load and inflation pressure. This measures variation in forces that would be exerted against the road. Next the tire is balanced using a balance machine.
This is a somewhat simple explanation of the manufacturing process for a tire and there are MANY details that are not covered here but when these steps are followed as specified, they translate to a completed tire.